Apparatus for drying fibrous webs on external drums



March 31, 1970 R. P. MAHONEY APPARATUS FOR DRYING FIBROUS WEBS ON EXTERNAL DRUMS 2 Sheets-Sheet 1 Filed March 11, 1968 INVENTOR.

RALPH P M/M/O/VE'Y Z ATTORNEYS March 31, 1970 R. P. MAHONEY 3,503,139

APPARATUS FOR DRYING FIBROUS WEBS ON EXTERNAL DRUMS Filed March 11, 1968 3 Sheets-Sheet 2 1' m m L1 7 INVENTOR.

1? P [fa/2022 f U 5g g ATTORNEYS United States Patent Int. Cl. F26b 11/04 U.S. Cl. 34111 12 Claims ABSTRACT OF THE DISCLOSURE Drying apparatus for fibrous webs such as coated and uncoated paper sheets. A felt is in direct contact with the dryer drum and forms a porous backing for the web when traveling about the dryer drum. In one drying application the felt is in the form of a loop and serves as a carrier to carry the moist paper Web to the dryer drum. In another drying application, particularly adapted for drying uncoated papers, at least two parallel spaced rows of dryer drums are provided, with the drums of one row between the drums of the other row. The dryer drums in one row are heated to a much higher temperature than the dryer drums in the other row. A felt in the form of a continuous loop is trained in a serpentine path alternately about the drums of each row of dryer drums. The felt and dryer drums form a guide to train the fibrous Web alternately under the felt about the drums of lower temperature and over the felt about the drums of higher temperature. A hood extends over the drums of higher temperature to remove moisture laden air from the web and felt. The hood may also impinge heated air on the web.

BACKGROUND OF THE INVENTION The dryer of the present invention improves upon conventional paper machine dryers, which usually consist of a series of rotatable dryer drums arranged one after the other in two vertically spaced horizontally extending rows. Separate felt runs are provided for the rows of upper and lower dryer drums, to hold the fibrous web to the drums as it travels about the drums from a lower to an upper drum and vice versa. A series of felt idlers has been provided between the rows of upper and lower dryer drums to retain the felt to pass about the respective rows of dryer drums over the web and to retain the web into direct contact with the dryer drums. In such dryers, the temperature of the dryer drums must be low enough to prevent cockle of the web, or tracking where the Web is coated. The heat of the dryer drums, therefore, is not high enough to dry the felt as it passes thereover and separate dryers must be provided for the felt.

The felt when holding the web to the hot dryer drums also retains the moisture from escaping from the paper, and whenever the paper is in direct contact with the dryer drum, the moisture has no place to go except into the felt. This causes cockle of the paper where the drums are too hot and causes tracking or streaking of the paper, where the paper is coated, resulting in such damage to the paper that it must be scrapped. Moreover, since the temperature of the dryer drums must be low enough to prevent cockle of the paper where the felt is over the sheet, the drying rate of conventional dryers is unduly long and requires a series of aligned dryer sections with 3,503,139 Patented Mar. 31, 1970 the fibrous web trained along the dryer drums of each dryer section from one end thereof to the other.

SUMMARY AND OBJECTS OF THE INVENTION With the dryer system of the present invention the felt may be trained in the form of a continuous loop in direct contact with a high temperature dryer drum. The dryer section may also include one row of dryer drums of a dryer section heated to a low temperature and a next adjacent row of dryer drums of the same dryer section, heated to a high temperature. A single continuous endless felt is trained alternately about the dryer drums of low and high temperature under the web when passing about the drums of high temperature and over the web when passing about the drums of low temperature. This results in much higher drying rates, due to the ability of the hot felt to absorb the moisture under the Web and thereby decrease the drying time and eliminate the requirement for felt dryers as well as felt idlers, heretofore necessary to wrap the felt about the dryer drums.

Also since the felt is under the web when passing about the high temperature drying cylinders there is no area of trapped moisture or gas at the tangent point between the sheet and drying cylinders, with the resultant elimination or tracking where coated-papers or webs are being dried, and a reduction in cockle of the Web caused by trapped moisture and gas, and a better frictional contact between the felt and web then between the web and dryer.

This apparatus is particularly advantageous for light weight sheets, since the dryer drums in direct contact with the felt may be run at very high temperatures and the felt under the sheet provides a porous backing for the sheet which permits the moisture to escape and also reduces the Bernoulli effect causing the web to be lifted up, when using air cap.

A principal object of the present invention, therefore, is to provide an improved form of dryer for fibrous webs and the like, arranged with a view toward eliminating defects in the paper and increasing the quality of the paper, as well as simplifying the form of the dryer.

Another object of the invention is to improve upon the efficiency in the drying of fibrous webs by training a felt about a high temperature dryer drum in direct contact with the drum to serve as a porous backing for the web as it passes about the drum, and to prevent the trapping and blowing of air under the web.

Another object of the invention is to provide an improved form of dryer for paper and the like, in which a single felt is used for the upper and lower rows of dryer drums of a dryer section, and the moist fibrous web is alternately passed under and over the felt, to accommodate the use of higher temperautre dryer drums where the web is passing over the felt and provide an area for the escape of moisture from the web.

Another object of the invention is to provide a novel form of dryer, shortening the drying time and preventing cockle and tracking of the fibrous web being dried, by providing at least one high temperature dryer drum, and holding the fibrous web from direct contact with the dryer drum by passing a felt in the form of a loop along the drum and guiding the web to pass along the outside of the felt.

Still another object of the invention is to reduce the number of drying sections in the dryer line for drying 3 I fibrous webs-by providing a row of high temperature dryer drums and-a second row of low-temperature dryer drums spaced from and between the high temperature dryer drums by passing a continuous felt alternately along the low and high temperature dryer drums and guiding the web to pass under the felt when passing along the low temperature dryer drums and over the felt while passing along the high temperature dryer drums, to effect absorption of moisture in the felt and the escape of moist air directly from the web.

, Still another object of the invention is to provide a noval apparatus for drying .fibrous webs in which the moist paper is passed along a series of dryer drums arranged in rows, one row of which dryer drums is of a higher temperature than the dryer drums of the other row, and in which the dryer drums are wrapped by a felt arranged in a serpentine path and the web is guided to pass under the felt when passing along the low temperature dryertdrums and over the felt when passing along the high temperature dryer drums to eliminate defects in the paper and increase the quality of the resultant paper.

These and other objects of the invention will appear from time to time as the following specification proceeds and with reference the accompanying drawings.

FIGURE 1 of the drawings diagrammatically shows a paper dryer section constructed in accordance with the principles of the present invention; and

FIGURE 2 diagrammatically illustrates the principles of the present invention applied to the drying of coated paper.

In FIGURE 1 of the drawings, a dryer section of a paper machine is diagrammatically shown in which a paper web W, travels from left to right and is trained in a serpentine path to pass around a lower dryer drum 11 of a row of successively arranged dryer drums 11, and upwardly and partially around an upper dryer drum 12 of a row of successively arranged dryer drums 12.

A felt 15 for encouraging evaporation of moisture from the web is trained in the form of a loop to pass in a serpentine path partially around the upper and lower dryer drums from one end of the dryer section to the other, and back to the first dryer drum of the bank of dryer drums. A material such as a foraminous plastic wire or a fabric of the type known as Formex fabric, is a common material used for felt, although a dense felt may be used and is equally as efiective as an open type felt for many installations.

As shown in the drawings, the felt passes from an outgoing high temperature dryer drum 12 of a bank of dryer drums under and over a series of idlers 16, 16 about an idler 17 to and around a tension idler 18 and under and over idlers 19 and 20 to an incoming dryer drum 11. From the dryer drum 11, the felt passes partially around the dryer drum 12 to a next succeeding dryer drum 11 and alternately to the dryer drums 11 and 12 to the end of the bank of dryer drums.

The dryer drums 11 are low temperature dryer drums, and may be heated to a temperature of between'160 and 200 F. a temperature of 180 F. being a mean temperature which has been found to give good drying results in cooperation with the high temperature dryer drums 12. The high temperature dryer drums 12 may be heated to temperatures of the order of 300 F. The dryer drums 11 and 12 are heated in a conventionel manner and are driven by power in a suitable manner, which is not shown herein, since it is no part of the present invention. The dryer drums 11 and 12 cause the felt 15 and web W to pass partially under and over the successive dryer drums 11 and 12 in a serpentine path and to return the felt from a last dryer drum 12 to an incoming dryer drumll of the section of dryer drums shown. A conventional form of hood 21 extends partially about the dryer drums 12 and may have air circulation and withdrawal means associated therewith to remove moisture laden air from the web and felt. The hood 21 may also impinge heated air on the web and may be of a conventional form, so need not herein be shown or described further.

The web W is trained partially over an idler 23 and partially about a low temperature dryer drum 11 and is wrapped about the periphery of the low temperature drum by the felt 15. As the web leaves the low temperature dryer drum 11, it passes to and about the next adjacent high temperature dryer drum 12 along the outside of the web, which is in direct contact with the high temperature dryer drum, to accommodate the felt to absorb moisture in the web and also to accommodate moisture to escape from the web W and be drawn into the hood 21. The web W thus passes over the felt about the first or incoming dryer drum 12 of the bank of dryer drums and downwardly to a second dryer drum 11 of the lower bank of dryer drums, under the felt in direct contact with the dryer drum, and

alternately to the high temperature and low temperature dryer drums of a first bank of dryer drums.

From the outgoing dryer drum 12 of the first bank of dryer drums the web W passes inwardly and downwardly along the outside of a felt 15 to and around an incoming high temperature dryer drum 12 of a second section of dryer drums. The second section of dryer drums is exactly like the first section, except the high temperature dryer drums are beneath the low temperature dryer drums to accommodate the passage of the web along the outsides of the felts 15 and 15 to and around an incoming high temperature dryer drum of a second bank of dryer drums. From the dryer drum 12 the web on the outside of the felt 15 then passes between the periphery of a low temperature dryer drum 11 and the felt 15 and continues its serpentine path around alternate high temperature and low temperature dryer drums on the inside of the felt as it passes along the low temperature dryer drums and on the outside of the felt as it passes along the high temperature dryer drums.

In the form of the invention illustrated in FIGURE 2 a paper web W is supplied to a conventional coating device 25, diagrammatically shown as being in the form of an applicator roll 26 rotatably driven to pick up coating solution in a coating bath pan 27 and apply the coating solution to the web as it passes thereover. The web then passes about a back-up roller 29 where excess coating is removed from the web W by an air knife 30. The coater and air knife are conventional so need not herein be shown or described further. The web then passes under a series of infrared dryers 31 into contact with a felt 33 on a direction changing guide roll 35.

The felt 33 is in the form of an endless belt or loop and is trained around the guide roll 35 and around a dryer drum 36, which may be heated to a temperature in the range of between 250 and 300 F. Fromthe dryer drum 36, the felt 33 passes around an idler 37 and tension roll 38 back to the direction changing roll 35.

Two air caps 39 are shown as extending along the outside of the felt and web from the direction changing roll 35 to the dryer drum 36. These air caps are conventional and impinge heated air on the web and felt, as the web is carried by the felt, from the direction changing roll 35, to the dryer drum 36. The temperature of the air impinged on the web by the air caps may be in the range of 200 to 600 F.

The dryer drum 36 is also diagrammatically shown as having an air cap 40 extending partially thereabout and impinging heated air on the web as it passes about the dryer drum, heated to a temperature range of between 200 and 600 F., depending on the type of material being dried and the speed of travel of the web and felt.

The temperature ranges mentioned are for illustrative purposes only and may vary in accordance with particular drying requirements.

From the dryer drum 36 the web W passes away from the dryer drum about an idler 41 and downwardly therefrom about a second idler 43. From thence the web W may pass through a conventional dryer section and then to a gloss calender for finishing.

With the structure just described, the felt 33 serves as a carrier for the web W around the direction changing idler 35 and under the air caps 39, and serves as a porous backing for the sheet as it passes about the dryer drum 36.

This prevents trapping of the air under the sheet as it comes onto the dryer drum, and when an air cap is used, prevents blowing of the air under the sheet at the edges of the sheet, and also prevents condensation of gases on the surface of the dryer drum from causing uneven drying across the dryer drum, the felt providing a convenient space for these troublesome gases and air and avoiding tracking of the coated paper.

The system just described thus avoids cockle of the coated sheet caused by the trapping of air under the sheet at the tangent point between the sheet and cylinder, by the blowing of air under the sheet and by uneven drying across the dryer drum.

It may be seen from the foregoing that a simplified form of dryer section for drying fibrous webs, such as paper and the like, has been provided, which enables drying at much higher drying temperatures than formerly, by running the felt about high temperature dryer drums and passing the moist fibrous we b along the outside of the felt while passing around the high temperature dryer drums, to provide for the free dissipation of moisture and gases into the hot felt and for the free escape of moisture from the web and felt. It may further be seen that in drying coated paper by the method and apparatus of the present invention, the web being out of contact with the hot dryer drum and the moisture and gases being absorbed in the hot felt and allowed to freely pass from the web, tracking or streaking of the paper, common in the drying of coated papers is eliminated and the resultant paper may be of such a high quality that calendering can be dispensed with in many instances.

It may further be seen that the passing of the web along the outside of the hot felt and the dissipation of moisture and gases into the felt, further prevents cockle of the web and particularly thin webs such as tissue paper and the like, which frequently occurs when the web is in direct contact with the heated surface of the dryer drum and is retained to the dryer drum by the felt.

It may also be seen that the dryer drum of the present invention results in more eflicient drying of the web in shorter time intervals than formerly, and eliminates the necessity of providing separate dryers for the felts, and obviates the need for felt idlers between the dryer drums.

While I have herein shown and described one form in which the invention may be embodied, it may readily be understood that various variations and modifications in the invention may be attained without departing from the spirit and scope of the novel concepts thereof.

I claim as my invention:

1. An apparatus for drying fibrous we'bs, such as paper and the like comprising,

at least one rotatably driven high temperature dryer drum, a felt, means training the felt to pass partially about the periphery of said high temperature dryer drum,

and means training a moist fibrous web to pass partially about the periphery of said high temperature dryer drum on the outside of the felt in intimate contact therewith, to effect the free escape of moisture from the web into the felt and from the outer surface of the web and means impinging heated air on the web while in intimate contact with the outer surface of the felt.

2. An apparatus for drying fibrous webs in accordance with claim 1,

wherein at least one lower temperature dryer drum is in association with the high temperature dryer drum,

wherein means are provided for training the felt alternately about said lower temperature drum and said high temperature dryer drum, and

wherein means are provided for training the moist fibrous web partially about said low and high temperature drums on the inside of the felt when traveling about the low temperature dryer drum and on the outside of the felt when traveling about the high temperature dryer drum.

3. The apparatus of claim 2, wherein the high temperature dryer drum is maintained at a temperature of the order of 300 F. and the low temperature dryer drum is maintained at a temperature of the order of 180 F.

4. In an apparatus for drying fibrous webs, such as paper and the like, a dryer section including a row of high temperature dryer drums,

a felt,

means passing the felt over said high temperature dryer drums for a portion of the circumference thereof and in direct contact therewith,

and means passing the fibrous web over and in intimate contact with the outer surf-ace of the felt as the felt and web pass over and partially about the high temperature dryer drums. 5. A drying apparatus in accordance with claim 4, wherein a second row of dryer drums is provided and extends parallel to the first row of dryer drums and is spaced between the first row of dryer drums and trains the felt and web to pass alternately around portions of the dryer drums of the first and second rows of dryer drums in a serpentine path, wherein the dryer drums of the second row of dryer drums are heated to a lower temperature than the dryer drums of the first row of dryer drums.

wherein the web is trained to pass under the felt when passing about the dryer drums of the second row of dryer drums, and over the felt when passing about the dryer drums of the first row of dryer drums, and

wherein means are provided for impinging heated air on the web while passing partially about the high temperature dryer drums in intimate contact with the outer surface of the felt.

'6. The apparatus of claim 5, wherein the felt is in the form of a continuous loop trained to pass partially about an incoming dryer drum of a row of low temperature dryer drums and an incoming dryer drum of a next adjacent row of high temperature dryer drums and alternately about the next succeeding dryer drums of each row of dryer drums in a serpentine path and to pass from the outgoing dryer drum of one row of dryer drums back to the incoming dryer drum of the first row of dryer drums.

7. A drying apparatus in accordance with claim '6,

wherein a second dryer section forms a continuation of the first dryer section,

wherein the high and low temperature dryer drums of the second dryer section are arranged oppositely from the high and low temperature dryer drums of the first dryer section, and have a felt trained partially therea'bout in a serpentine path from one end of said second section to the other, and

wherein the web is trained to pass between the felts of the first and second dryer section, along the outside of the felt of the second dryer section when passing from one dryer section to the other.

8. An apparatus particularly adapted for drying coated webs comprising,

a rotatably driven heated dryer drum,

a felt wrapped about said dryer drum,

and means training a moist coated web to pass about the periphery of said drum on the outside of said felt and in intimate contact with the outside of the felt to provide a porous backing for the web and effect the free escape of moisture into the felt and from the outer surface of the web.

9. An apparatus particularly adapted for drying coated paper webs in accordance with claim 8, wherein an air cap extends partially about said dryer drum and impinges heated air on the web.

10. An apparatus particularly adapted for drying coated paper Webs in accordance with claim 8,

wherein the felt is in the form of a closed loop, wherein a direction changing idler spaced from the dryer drum is provided to train the felt to and from the dryer drum, whereby the felt serves as a carrier for the moist web to the dryer drum, and serves as a porous backing for the web when traveling about the dryer drum. 11. An apparatus particularly adapted for drying coated paper webs in accordance with claim 10, wherein an air cap extends partially about said dryer drum and impinges heated air on the web.

12. An apparatus particularly adapted for drying coated paper we bs in accordance with claim 11, wherein at least one air cap extends along the felt and web as the felt carries the web from the direction changing idler to the dryer drum, and impinges heated air thereon.

References Cited UNITED STATES PATENTS 976,948 11/1910 Tompkins 34- 111 X JOHN I. CAMBY, Primary Examiner 

